The present invention relates to an ink jet recording head, which is a minute droplet jetting device which jets and shoots a recording liquid, called ink, as minute droplets onto a recording sheet to record an image on the sheet, and an ink jet recording apparatus equipped with such a recording head.
FIG. 1 is a developed perspective view showing an example of the construction of a conventional ink jet recording head.
In this recording head, an energy generating element 12 is provided on a substrate 11 made of glass or ceramics, and an ink path 15 in which the energy generating element 12 is provided, an ink jetting nozzle 14, and a common ink reservoir 16 from which ink is supplied to the ink path 15, are formed from a hardened light sensitive resin film 13 according to a photolithography method. The resulting hardened light sensitive resin film 13 is laminated with the upper plate 17 composed of for example, glass, ceramics or metal through an adhesive layer 19.
In the recording head having such construction, the liquid repellent property of the outer surfaces of the substrate 11, the hardened light sensitive resin film 13, and the upper plate 17, each surrounding the ink jetting nozzle 14, is extremely important in stably jetting ink from the ink jetting nozzle 14. If ink flows to the outer surface of the peripheral area of the ink jetting nozzle 14 or adheres thereto to produce a pool of ink there, there may occur an undesirable phenomenon that the ink jetting direction deviates from a given direction in jetting ink from the ink jetting nozzle 14 and further fluctuates every ink jet due to instability of the pool of ink, resulting in inability of stable ink jetting or good image recording.
When the peripheral area of the ink jetting nozzle is covered with ink, ink scatters on ink jetting, and stable recording cannot be carried out. When a pool of ink formed at the peripheral area of the ink jetting nozzle becomes large, ink jetting from the ink jet recording head becomes next to impossible.
The above-described phenomenon can occur in the ink jet recording head having a construction as illustrated in FIG. 2, in which a nozzle plate 21, that is, a thin plate of plastic or metal of an appropriate thickness having orifices (nozzles) 22 of the same number as ink paths 15 of the ink recording head, is additionally adhered to the surface on the side of the ink jetting nozzle 14 of the ink path. In this construction the peripheral area of the ink jetting nozzle is the peripheral area of the nozzles on the outer surface of the additionally provided nozzle plate.
There is also an ink recording head as shown in FIG. 3 in which an upper plate 17 having a common ink reservoir 16, an ink path 15, and an ink jetting nozzle 22 as one body is laminated onto a substrate 11 having an energy generating element 12. The upper plate used in such a construction can be composed of polysulfones, polyethersulfones, polyesters or polyacetals. Further, there is also another ink jet recording head having a construction as shown in FIG. 4, in which an upper plate 46 made of ceramic with a common ink reservoir 47 is adhered to a piezoceramic 41 with an ink path 44 formed by an engraving method, and a nozzle plate 52 is adhered to the ink jetting nozzle side of the ink path 44. The ink jet recording apparatus having such a construction also has a peripheral area of an ink jetting nozzle.
As a method of solving the above problems, there is a proposal which is disclosed in Japanese Patent O.P.I. Publication Nos. 56-89569, 62-55154, 2-153744 and 4-211959 that a coat layer (being a water repellent layer) is provided at least on the outer surface of the peripheral area of the ink jetting nozzle 14 as shown in FIG. 5. In such a technique, silicone type polymers or oligomers, or fluorine-containing polymers or oligomers are used as the water repellent layer.
In the ink jet recording head of the ink jet recording apparatus, the peripheral area of the ink jetting nozzle is always contact with ink, and is usually positioned in a dusty atmosphere, in which dust is produced for example, from the recording paper sheets. Therefore, in order to provide stable ink jetting, the peripheral area of the ink jetting nozzle is required to be wiped with a rubber blade or a sponge for cleaning and thereby kept clean. Further, in order to prevent clogging of the ink jetting nozzle due to dried ink, the ink jet recording head is required to be covered with a cap comprised of a rubber during non-operation. The coverage also prevents ink from evaporating from the ink jetting nozzle. When the ink jetting nozzle of the ink jet recording head is clogged with clogging matter, the clogging matter needs to be removed by applying a means for sucking to the peripheral area of the ink jetting nozzle.
These processes apply stress such as mechanical abrasion, pressure, stretching or peeling to the peripheral area of the ink jetting nozzle of the ink jet recording head. Therefore, the liquid repellent layer provided at the peripheral area of the ink jetting nozzle is required to have sufficient abrasion resistance, sufficient mechanical strength, or sufficient adhesion strength, and to maintain these effects for a long time without being peeled from the peripheral area of the ink jetting nozzle comprised of various materials.
Fluorine-containing polymers or oligomers conventionally used are insufficient in anti-abrasion or mechanical strength on account of substantially low value of its cohesion energy density, and insufficient in adhesion strength on account of substantially low value of its surface energy. Accordingly, they cannot maintain their liquid repellent property for a long time.
Some liquid repellent agents of a silicone type conventionally used provide improved adhesion property, but are insufficient in mechanical strength, particularly in an anti-abrasion property.
In the liquid repellent layer which is insufficient in abrasion resistance, mechanical strength, or adhesion strength, broken pieces, peeled from the peripheral area of the ink jetting nozzle, may be pushed into the ink jetting nozzle by wiping for cleaning, resulting in clogging the whole of the ink jetting nozzle and in inability of ink jetting. Alternatively, the broken pieces clog partially the ink jetting nozzle, resulting in deviation of the prescribed ink jetting direction or in reduction of the prescribed ink jetting amount.
When mechanical peeling occurs at a part of the peripheral area of the ink jetting nozzle, affinity of the peeled portions to liquid ink increases and causes deviation of the ink jetting direction.
These cause deterioration of recording image quality, resulting, at the worst in inability of recording.
It is another important matter for the ink repellent layer used in the ink jet recording head that the ink repellent property of the layer is not lowered even when the layer is in contact with ink for a long time.
When the liquid repellent layer is repeatedly brought into contact with ink, or when the liquid repellent layer is wiped with a rubber blade, for example for cleaning while it is in contact with ink, the liquid repellent property of the layer is lowered in many cases due to interaction between materials constituting the liquid repellent layer and materials constituting ink.
Particularly, silicone type polymers have the tendency described above, and when such silicone type polymers are brought into contact with a certain kind of ink, they may rapidly lose their liquid repellent property.
Fluorine-containing polymers cannot be freed from such a tendency, and there are no fluorine-containing polymers maintaining the initial liquid repellent property after being wiped with a rubber blade during repeated contact with ink.
When the liquid repellent property of the liquid repellent layer is lost, problems occur such that the ink jetting direction deviates from a given direction or ink scatters every ink jetting as when the liquid repellent layer is mechanically broken as described above. When the whole peripheral area of the ink jetting nozzle is covered with ink, ink scatters on ink jetting, resulting in inability of stable recording. The liquid repellent property can be generally represented by a contact angle, particularly a regress contact angle, and more practically, it is represented by the slip property of ink when an ink of a specific composition is used.
An object of the invention is to provide an ink jet recording head capable of stably jetting ink in a substantially constant amount in the prescribed direction, and an ink jet recording apparatus employing the ink jet recording head.